One of the few regions of HIV capable of eliciting neutralizing immune responses against primary isolates of HIV is the ELDKWA epitope (named for its amino acid sequence) on the exterior domain of the gp41 protein. While not all infected individuals respond immunologically to this highly conserved region, those who do are more likely to have favorable health characteristics and a reduced likelihood of transmitting HIV to offspring, highlighting the importance of targeting this region of HIV for vaccine purposes. In this work, we propose to construct combinatorial libraries that systematically present this epitope in a diverse array of conformations on a naturally immunogenic surface loop of the cold causing human rhinovirus. The ELDKWA sequence will be flanked by linkers of varying lengths and sequences as well as by cysteine residues with the potential to form disulfide bonds. We propose to make a fraction of the enormous number of potential chimeras in this library as well as four libraries that are specific subsets of the parent library that will encode ELDKWA presentations analogous to those of a parallel set of ELDKWA presenting constrained peptides being synthesized in the laboratory of Professor John Taylor at Rutgers University. Chimeras with immunologically relevant presentations of the ELDKWA sequence will be selected for their abilities to be recognized by the neutralizing human monoclonal antibody 2F5. Using these methods, we have been able to elicit some of the potent neutralizing immune responses reported against the HIV-1 V3 loop. A subset of the immunoselected viruses will be tested for reactivity with 2F5 and HIV IG (using ELISAs and BIAcore experiments) and chimeric viruses will be tested for their ability to be neutralized by 2F5 and HIV IG as well. Chimeras of greatest interest will be used to immunize guinea pigs to assess their ability to elicit anti-HIV-1 neutralizing responses against diverse laboratory and primary isolates of HIV-1. The affinity and neutralization data will be used to guide the design of second generation virus libraries (and peptides) to be made and characterized in the second year of this grant. It is our hope that such a systematic approach to the design of immunogenic presentations of ELDKWA will lead to the identification of immunogens that will be able to elicit robust, consistent, and cross-reactive immune responses to HIV.